Horses' Grass Choices Depend on Nutritional Value (FRA)

Give your horse two choices: tall grass or low grass. Which one will he choose?

That answer depends a lot on the quality and nutritional composition of the grass, according to a new study by French researchers.

Although horses select the tallest grass when the quality of turfs is equally good, their main objective appears to be efficient intake of major nutrients, especially digestible protein, the researchers reported.

"Horses seem to be capable of adjusting their feeding behaviors (grazing time, speed of ingestion, choice of feeding sites) in response to variations in availability and quality of pasture vegetation in order to cover their nutritional needs," said Géraldine Fleurance, PhD, researcher for the French Horse and Equitation Institute (formerly the French national stud) and the National Institute for Agricultural Research (INRA) in Saint-Genès-Champanelle and a primary author of the study.

During their research, Fleurance and her team presented 2-year-old fillies with various trays of freshly removed grass turfs (including 10 cm of topsoil). In one experiment, the horses could choose between tall and low grass, both of good quality. In a second experiment, the horses received two choices among the following combinations: tall grass of poor quality, medium grass of medium quality, and short grass of high quality.

What the horses chose depended on the nutritional content, Fleurance said. "In the first experiment, digestible protein was not limiting, and the horses selected patches of tall grass where food was ingested faster. But in the second experiment, they maximized their protein intake rate by selecting shorter turfs when the protein supplies declined in the taller ones."

The horses spent about 70% of their feeding time on the shorter alternatives, Fleurance added. They also chewed as much as 45% less before swallowing. "They're maximizing their intake of digestible protein while minimizing the (energy) costs," she said.

Even so, their choices were not definitive, according to Fleurance. "The shorter turfs provided higher rates of digestible protein intake, but their net energy was lower (compared to the taller turfs)," Fleurance said while presenting her results at the 2010 Equine Research Day in Paris. "So the horses may have been balancing their protein and energy intake by feeding off both turfs."